a few simple questions

[Tony Clark]

> And by the way, most opamps (all types that I use) can't go from rail
> to rail.  I.e. +-15V is not possible with +-15V supply, you can get at
> most ~ 13V.  The 10V thing seems to be a tradition from old analog
> computing.  And another argument: a vco with 1V/octave (another
> standard, I think from Moog and ARP) needs 10V for a sweep of 1:1024 and
> this is about the width you need for sweeping across the entire audio
> band.

   Most Rail-to-rail op-amps can't handle +-15V!

> But CVs usually don't go and should not go from -5 to +5V. Most VCA
> designs need 0-10V. What I want to say is that CVs should have at least
> a max. peak-to-peak value of 10V, but some offset can be added
> before/after attenuation.

   Not normally, no.  This is somewhat of a design limitation, really.  
Although most VCA's may _need_ 0-10V, it only takes one opamp with a -5V 
bias to translate that to a +-5V input.  One prime example of this sort 
of setup is the Korg polyphonic modulars.  All of the patchable signals 
are +-5V (+-3V in some cases).  Of course they don't have patchable 
audio!

   Tony

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I can't drive (my Moog) 55!         |     The E-Music DIY Archive
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Tony Clark -- clark at andrews.edu     | aupe.phys.andrews.edu/diy_archive
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